According to modern medical techniques, certain chronic diseases may be treated by delivering a medication or other substance to the body of a patient. For example, diabetes is a chronic disease that is commonly treated by delivering defined amounts of insulin to a patient at appropriate times. Traditionally, manually operated syringes and insulin pens have been employed for delivering insulin to a patient. More recently, modern systems have been designed to include programmable pumps for delivering controlled amounts of medication to a patient.
Pump type delivery devices have been configured in external devices, which connect to a patient, and have also been configured in implantable devices, which are implanted inside of the body of a patient. External pump type delivery devices include devices designed for use in a stationary location, such as a hospital, a clinic, or the like, and further include devices configured for ambulatory or portable use, such as devices that are designed to be carried by a patient, or the like. External pump type delivery devices may contain reservoirs of fluidic media, such as, but is not limited to, insulin. External pump type delivery devices may be connected in fluid flow communication to a patient or user, for example, through a suitable hollow tubing. The hollow tubing may be connected to a hollow needle that is designed to pierce the skin of the patient and to deliver fluidic media there through. Alternatively, the hollow tubing may be connected directly to the patient as through a cannula, or the like.
Examples of some external pump type delivery devices are described in the following references: (i) Published PCT Application WO 01/70307 (PCT/US01/09139), entitled “Exchangeable Electronic Cards for Infusion Devices”; (ii) Published PCT Application WO 04/030716 (PCT/US2003/028769), entitled “Components and Methods for Patient Infusion Device”; (iii) Published PCT Application WO 04/030717 (PCT/US2003/029019), entitled “Dispenser Components and Methods for Infusion Device”; (iv) U.S. Patent Application Pub. No. 2005/0065760, entitled “Method for Advising Patients Concerning Doses Of Insulin”; and (v) U.S. Pat. No. 6,589,229, entitled “Wearable Self-Contained Drug Infusion Device”, each of which is incorporated by reference herein in its entirety.
As compared to syringes and insulin pens, pump type delivery devices can be significantly more convenient to a patient, in that doses of insulin may be calculated and delivered automatically to a patient at any time during the day or night. Furthermore, when used in conjunction with glucose sensors or monitors, insulin pumps may be automatically controlled to provide appropriate doses of fluidic media at appropriate times of need, based on sensed or monitored levels of blood glucose. As a result, pump type delivery devices have become an important aspect of modern medical treatments of various types of medical conditions, such as diabetes, and the like. As pump technologies improve and doctors and patients become more familiar with such devices, external medical infusion pump treatments are expected to increase in popularity and are expected to increase substantially in number over the next decade.
However, one of the problems with pump type delivery devices is that a bolus of fluidic media could be delivered inadvertently to the patient in a case where the reservoir of fluidic media is pressurized. FIG. 13 illustrates a conventional reservoir system 700. The reservoir system 700 may include a reservoir 710 with an interior volume 715 filled with fluidic media, a plunger head 720, a plunger shaft 725, and a driveshaft 772 mechanically connected to a drive motor 774. The reservoir 710 may include a self-sealing septum 711. When the reservoir 710 is inserted in the reservoir system 700, the plunger shaft 725 mechanically couples with the driveshaft 772 by use of complementing mating parts, such as threads, for example. If the complementing threads of the plunger shaft 725 and the driveshaft 772 are not perfectly aligned, the plunger shaft 725 shifts a small distance, such as a half thread forward or backward, so that the threads can align and couple together. Accordingly, the plunger head 720, which is connected to the plunger shaft 725, is moved a half thread forward or backward within the reservoir 710. If the plunger head 720 is moved forward, pressure in the interior volume 715 of the reservoir 710 is increased. As a result, this could cause the reservoir system 700 inadvertently to pump a small bolus of fluidic media to a user once a fluid path between the reservoir system 700 and the user is established. Alternatively, the interior volume 715 of the reservoir 710 could become pressurized due to a change in an external influence such as an altitude or a temperature as well, which could also lead to an inadvertent bolus of fluid being delivered to the user once the fluid path between the reservoir system 700 and the user is established. The opposite effect is true for a system that draws the plunger head backwards, establishing a negative pressure in the reservoir. In this case, bodily fluids may be drawn into the fluid path or reservoir when the fluid system is fully connected.